In semiconductor industry, including various types of semiconductor processing and manufacturing devices, an ever-increasing desire exists to manufacture smaller structures with high accuracy and reliability. Lithography is often a critical part of such manufacturing processes. During lithography exposure or other types of processing, the target (e.g. a semiconductor wafer) may need to be situated in a high vacuum environment that is hermetically sealed from the surroundings (e.g. from atmospheric conditions), to reduce the probability of contamination.
In the particular case where such vacuum environment is applied for operating a mask-less lithography system, charged particle beamlets may be used to transfer a pattern onto the target. The beamlets may be individually controllable to obtain the desired pattern. To be commercially viable, mask-less lithography systems need to meet challenging demands for wafer throughput and error margins. A higher throughput may be obtained by using more beamlets. The handling of a greater number of beamlets calls for more sophisticated control devices and circuitry, without compromising the necessary vacuum conditions or significantly increasing the required fab space (i.e. the area covered by the processing unit). The task of arranging more process control devices and/or circuitry in a decreasing available volume while maintaining hermetic seals between various parts of the lithography system becomes more and more challenging.
For the control of the lithography systems, including control of a large number of beamlets for exposing the target as well as various other control devices and circuitry, various types of signals, encompassing power supply signals, various electrical signals, and/or optical signals, have to be transmitted or passed through the boundary of the vacuum environment.
In relation to the technological subject of feedthrough of either signals or electric power from one environment or compartment to another, the publication “Hermetic Sealing with Epoxy” of W. D. Wood and W. L. Wood, Mechanical Engineering Vol. 112, March 1990, p. 46 (http://www.pavetechnologyco.com/pdf/hermetic.pdf), describes this as a long standing basic and generic technology, using glass or ceramic filled metal housings. The publication also describes a major development in this technology by the application of epoxy based sealing in bulk heads and other type of signal or power feedthrough from the early 1980's. The publication indicates that epoxy sealing provides good vacuum sealing in combination with various materials used in and/or around electrical conductors, including aluminum as widely used for creating vacuum environments, and copper as widely used for conveying electric signals, as well as various insulating materials. It is further indicated that epoxy seals comply with cleanliness requirements making them suitable for use in vacuum wafer-handling systems.
From the teaching of the article of Wood and Wood it may hence be concluded that epoxy sealing can be expected to be applicable also for hermetically sealing printed circuit boards (PCB) in an electrical feedthrough.
An example of such known type of PCB feedthrough using a bulkhead in combination with an O-ring is provided by patent document U.S. Pat. No. 6,305,975B1, which describes the feed through of a PCB permanently encapsulated in an epoxy based bulkhead. The PCB with bulkhead may in principle be formed as the cover for a cylindrically shaped opening of a low pressure chamber, and is at its perimeter sealed to the opening using an O-ring type of vacuum seal.
U.S. Pat. No. 7,164,142B2 shows examples of vacuum feedthrough including the known face type sealing. A structure for an electrical feedthrough is described, utilizing a sheet of insulating material including at least one embedded layer of conductive tracks, where the sheet face is sealed to the vacuum wall using a fillet of sealing material. PCB is indicated to form an example of such insulating material comprising a plurality of conductive tracks.
While the latter mentioned feedthrough of U.S. Pat. No. 7,164,142B2 merely seems to provide for permanent sealing of a PCB feedthrough, the older, in 2001 published U.S. Pat. No. 630,597B1 forms a more versatile design, providing a releasable PCB feedthrough connector.
U.S. Pat. No. 8,242,467B2, assigned to the current applicant, discloses a multi-beamlet lithography system. This system comprises a beamlet blanker (or modulator) for selectively allowing or denying individual beamlets passage to the target, based on pattern data. The beamlet blanker is arranged near the target in a vacuum chamber, but controlled by a control unit that is located outside the vacuum chamber. The lithography system includes an optic system with an array of optical fibers for transmitting modulated light signals with the pattern data from the control unit to light sensitive blanking actuators on the beamlet blanker. The fibers are routed via an opening in a feedthrough device through a wall of the vacuum chamber. Vacuum compatible sealing material is used to provide an airtight sealing for the fibers in the opening. U.S. Pat. No. 8,242,467B2 presents little details in relation to the structure of the feedthrough device.
Patent document US2016/0787599A1 describes fiber alignment assemblies for hermetically feeding optical fibers through a housing of an opto-electronic module. One such assembly includes a ferrule, with two adjoined ferrule portions. One ferrule portion has a surface with four alignment grooves, which accommodate end sections of optical fibers. The second ferrule portion covers the surface and the alignment grooves of the first ferrule portion, when the ferrule portions are mated together to form the ferrule. Sealant material, such as glass solder, may then be fed into the ferrule, through an aperture in one of the ferrule portions. Vacuum is applied to a pocket in the ferrule, to draw the glass solder through clearances between the optical fibers and grooves, to form a hermetic seal. The hermetic assemblies from US2016/0787599A1 are primarily suitable for feeding through relatively small numbers of individual optical fibers.
It would be desirable to provide a feedthrough device that is suitable for routing a large number of signal conductors, such as optical fibers (i.e. several tens or hundreds) or electrical conductors, for example provided in printed circuit boards, in an ordered and hermetically sealed manner through a structure that separates two regions with different ambient conditions.
It is also desirable to provide vacuum feedthrough devices which allow for reliability, versatility and repeatability in a contemporary industrial design.